Abstract: A balanced coil system (2) of a metal detection system has a transmitter coil (21) connected to a first transmitter unit (1), to provide a transmitter signal (s1) comprising at least first and second operating frequencies (fTX1, fTX2). First and second receiver coils (22, 23), which compensate one another when the system is in balance, provide output signals (s22, s23) to a receiver unit (3). The respective operating frequencies are applied separately together each with a monitoring frequency (fMON) to inputs of first and second modulation units (52, 53), which provide first and a second modulated monitoring signals (sM1, sM2), each comprising a first or second modulated monitoring frequency (fMM1, fMM2) without a carrier. When applied to a summation unit (54), the modulated monitoring signals result in a combined output signal (sM12) that is applied to a monitoring coil (24), inductively coupled with at least one of the receiver coils.

Abstract: A balanced coil system (2) of a metal detection system has a transmitter coil (21) connected to a first transmitter unit (1), to provide a transmitter signal (s1) comprising at least first and second operating frequencies (fTX1, fTX2). First and second receiver coils (22, 23), which compensate one another when the system is in balance, provide output signals (s22, s23) to a receiver unit (3). The respective operating frequencies are applied separately together each with a monitoring frequency (fMON) to inputs of first and second modulation units (52, 53), which provide first and a second modulated monitoring signals (sM1, sM2), each comprising a first or second modulated monitoring frequency (fMM1, fMM2) without a carrier. When applied to a summation unit (54), the modulated monitoring signals result in a combined output signal (sM12) that is applied to a monitoring coil (24), inductively coupled with at least one of the receiver coils.

Abstract: A method for operating a metal detection apparatus that comprises a transmitter unit with a drive circuit that alternately applies two different drive voltages via a first set of two drive switches to a first tail and via a second set of two drive switches to a second tail of a transmitter coil that is coupled to a receiver coil, which is connected to the input of a receiver unit. A system adapted to operate according to an exemplary method is also provided. In one embodiment, at least a first waveform is generated for controlling the first set of drive switches and at least a second waveform is generated for controlling the second set of drive switches, wherein the first and second waveforms that correspond to a selected operating frequency are shifted relative to one another in order to allow a desired drive current to flow through the transmitter coil.

Abstract: A method for operating a metal detection apparatus that comprises a transmitter unit with a drive circuit that alternately applies two different drive voltages via a first set of two drive switches to a first tail and via a second set of two drive switches to a second tail of a transmitter coil that is coupled to a receiver coil, which is connected to the input of a receiver unit. A system adapted to operate according to an exemplary method is also provided. In one embodiment, at least a first waveform is generated for controlling the first set of drive switches and at least a second waveform is generated for controlling the second set of drive switches, wherein the first and second waveforms that correspond to a selected operating frequency are shifted relative to one another in order to allow a desired drive current to flow through the transmitter coil.

Abstract: A method for monitoring the operation of a metal detection system that comprises a balanced coil system with a transmitter coil that is connected to a transmitter unit, which provides transmitter signals having a fixed or variable transmitter frequency, and with a first and a second receiver coil that provide output signals to a receiver unit. A system adapted to operate according to an exemplary method is also provided. According to one embodiment, a carrier signal having the transmitter frequency and a monitoring signal having a monitoring frequency are provided to a modulation unit that suppresses the carrier signal and provides a modulated monitoring signal, which is supplied to a monitoring coil that is inductively coupled with at least one of the receiver coils, whose output signals are demodulated in a demodulation unit that provides a demodulated monitoring signal, which is compared in phase and/or in amplitude with a reference.

Abstract: A method for operating of a metal detection system may comprise a balanced coil system with a transmitter coil that is connected to a transmitter unit, which generates transmitter signals having a transmitter frequency that is selected from a group of at least two transmitter frequencies, and with a first and a second receiver coil that provide output signals to a signal input of at least one amplifier unit included in a receiver unit, wherein the output signals compensate each other so that the system is in balance. A system adapted to operate according to an exemplary method is also provided.

Abstract: A method for monitoring the operation of a metal detection system that comprises a balanced coil system with a transmitter coil that is connected to a transmitter unit, which provides transmitter signals having a fixed or variable transmitter frequency, and with a first and a second receiver coil that provide output signals to a receiver unit. A system adapted to operate according to an exemplary method is also provided. According to one embodiment, a carrier signal having the transmitter frequency and a monitoring signal having a monitoring frequency are provided to a modulation unit that suppresses the carrier signal and provides a modulated monitoring signal, which is supplied to a monitoring coil that is inductively coupled with at least one of the receiver coils, whose output signals are demodulated in a demodulation unit that provides a demodulated monitoring signal, which is compared in phase and/or in amplitude with a reference.

Abstract: A method for operating of a metal detection system may comprise a balanced coil system with a transmitter coil that is connected to a transmitter unit, which generates transmitter signals having a transmitter frequency that is selected from a group of at least two transmitter frequencies, and with a first and a second receiver coil that provide output signals to a signal input of at least one amplifier unit included in a receiver unit, wherein the output signals compensate each other so that the system is in balance. A system adapted to operate according to an exemplary method is also provided.

Abstract: The invention concerns a method for characterizing the timbre of a time-varying sound signal s(t) using at least one descriptor, where the at least one descriptor includes a harmonic spectral spread of the sound signal s(t). The sound signal s(t) may be compared to other sound signals using the at least one descriptor. The at least one descriptor may also include a harmonic spectral deviation of the sound signal s(t).

Abstract: The invention concerns a method for characterizing in accordance with at least a descriptor, the timbre of a time-variable sound signal (s(t) for a duration D, which consists in defining said descriptor by the harmonic spectral scope of the signal.